Screw



seamed Dec. 14, 1931 setts 3 Claims.

My present invention relates to the so-called self-tapping type of screw, wherein the screw has a thread-cutting portion to be driven thru and into material as a fastening means; and more particularly this invention relates to a bluntended self-tapping screw with automatic centering means to be fitted to and driven in a preformed opening.

Thus, my improved screw has a thread-holding portion formed with complete uninterrupted threads extending from the head downwardly around the shank, and a thread-cutting portion with a plurality of cutting corners alternating without-away parts to provide spaces for the removal of the material out, together with a construction affording a tapering self-centering means to position the blunt end on a pre-formed recess into' which it is to be driven. The general object of the invention is to provide a novel and improved thread forming screw of this character, which may be economically manufactured and which is adapted to materially reduce the efiort and cost involved in assembling a great variety of manufactured articles and structures, especially those involving joining of sheet metal and making fastenings to sheet metal 'thru pre-formed openings in the material.

It is a more particular object of the invention to provide a thread forming fastening element of this character, theentering end of which is blunt to enter pre-formed openings, and provided with a plurality of cutting edges alternating with cutaway portions to provide spaces for the removal of the materialcooperating and designed to remove the metal or material of which the member to be secured is formed, in cutting the threads for the reception of the screw in a manner somewhat similar to that effected by an ordinary tap.

This manner of forming the threads is quite or forcing the metal or other material to one side as in the case of previously proposed thread form ing screws, Because of the cuttingaction of the present screw, it can'be driven with greater facility than in the case of the former type of screws referred to.

In the preferred'embodiment of my invention, there are provided a plurality, for example, of four cutting edges at the pilot or entering portion of the screw by means of cutting away or flattening the entering portion'on opposite, sides; which also provides four equally'spaced points at the entering end, serving to hold the screw firmlywithin the drilled or otherwise preformed hole provided in the work. These initial points of supdifferent from the process of upsetting, suaging,.

UNITED STATES PATENT-OFFICE Frank K Brown, South Dartmouth, Mass assignor. to Continental Screw Company, New 'Bediord, Maaa, a corporation oi Massachu- Original No. 2,062,550, dated December 1, 1936. Serial No. 734,034, July 6, 1934; Application :01- reissue March z, 1931, Serial No. 128,681.

port position the screw perpendicularly to the surface in which it is to be inserted and, during the cutting operation, all of these contacting points or cutting edges start cutting the material simultaneously, thus preventing the screw from tilting and permitting it to' be driven into the work in a straight line so thatgthe head is absolutely flush with the surface of the material when the screw is fully seated therein.

The principles of my invention are applicable to screws provided with either machine threads or threads of the wood screw type.

As suggested in the drawing and specification, the flattening of the entering end of the screw may take two forms, either one in which plane surfaces are formed at equal intervals around the entering end of the screw and providing a square entering end, or one in which the flattening or attenuation of the screw is attained by the formation of concavities at equally spaced areasaround the entering portion.

Needless to state, the screws formed in accordance with the present inventibn may be tempered or hardened to any degreenecessary depending upon the nature and character of the work to which theyare to be applied.

Other objects and features of novelty will be apparent from the following specification when read in connection with the accompanying drawing in which certain embodiments oi my invention are illustrated by way of example.

In the drawing Fig. 1 is a view in side elevation of a machine screw embodying the principlesof my invention, and illustrating the application of the thread forming screw to the material to be threaded and secured; the flnal'pos'ition of thetwo sheet metal members, which are fastened together in this example being shown in dotted lines;

Fig. 2 is an end view of the screw illustrated in Fig. 1;

Fig. 3 is with wood screw threads embodying the principles of my invention and which has been applied to a pair of sheet metal elements;

Fig. 4 is an end view of the screw .in Fig. 3;

illustrated a view in side elevation of the screw Fig. 5 is a view in perspective of the screw view of the screw shown in Referring more particularly to Figs. 1 and 2 of the drawing in which the machine screw embodiment is illustrated, it will be seen that the .screw is indicated generally by the numeral ill and is provided with a threaded shank H and a head I! which may be of any desired configuration, but is shown by way of example as a round head. In all cases it is preferred that the threads be carried all the way to the head of the screw. The entering face it of the screw is'preferablyflat and the contour of this entering face is rendered substantially square, as'clearly shown in Fig. 2 of the drawing by the flattening of the entering portion of the screw on four diametrically opposite sides as indicated at I. This flattening may be applied by grinding, planin Dressing, or

hammeringas desired, and it aflects the coreor body portion of this end of the shank as well as the threads thereof.

The threaded lands which lie between the flattened areas are indicated by the numerals ii and are preferablygtapered slightly toward the entering end of the screw so as to terminate in the points I8 which form the corners of the squared end surface ll. 'Ihis tapering of the threaded lands, of course, diminishes the height of the threads progressively toward the enteringend of the screw and enables this end to be inserted in the opening in the work already formed. by drilling or otherwise. Such an opening is indicated at I! in the metal sheet 2! illustrated in Fig. 1. The conformation of the entering and of the screw as thus described is somewhat similar to that of an ordinary tap which has long been emat equal intervals around the entering end of the screw will serve to center the screw in the opening.

such as [9, during the initial application. Then upon rotation of the screw the leading edges 22 of the threaded lands It will start cutting the rim of the opening it and thethreads of gradually increasing height on these lands will progressively cut corresponding female threads in the material 20 until the full depth of thread is reached at the point 23. Rotation of the screw.- however, is continued in most cases until the entire shank has entered the material and the head rests flush with the outer surface thereof, as indicated in certain of the figures of the. drawing. In many cases, not only when the screw is used in soft material, such as wood or the like, but in uniting sheet metal or other relatively hard material, it may be desirable to employ a screw of the wood screw type such as illustrated at 25 in Figs. 3 and 4 of the drawing. The head 28 of the screw 25 is of' the binding head type but, of course, may be of any desired configuration such as one of the following types: round head, binding head, stove head, or counter-sunk heads of different varieties. The entering or pilot end of the screw 25 is flattened, preferably on the four diametrically opposite sides as at 21 in a manner similar to that applied to themachine screw illustrated in Figs. 1 and 2. The threads are progressively diminished in depth on the lands II as in the previously described embodiment and the application of the embodiment last described to opposite plane surfaces is less than the root 'ous threads throughout the greater length of said shank, a. blunt rectangular entering end thread-holding portion is provided.

configuration of the end face 29.01! the screw/is also that of a square having the four'corners 3B which are adapted to center the screw during its initial application. to the work. Similarly, the advancing cutting edges 3|-of the lands 28 cut their way into the stock and form the threads into which the screw progressively moves. Two metal sheets 33 are shown in Fig. 3 as being joined by a screw of this type.

In Fig. 5 of the drawing a screw such as illustrated and described in connection with Figs. 1 and 2 is shown in perspective. I

In the embodiment illustrated in Figs. 6 and '7 the wood screw 35 is provided with concave depressions 36 in lieu of the flattened areas I! and 21 applied in the other modifications. This form ofscrew may be employed when a slightly sharper cutting edge?! is desired. The configuration of the face 38 of the entering end of the screw is that of a square with arcuate inwardly curved,

or bowed sides and rather acute corners iii. The

the work is exactly the same as in the case of the earlier modifications.

It will be understood that various changes and modifications may be made in the embodiments Y illustrated and described herein without departing from the scope of the invention as defined in the following claims.

I claim:

1-. A thread cutting and fastening screw adaptcluding the shank and the thread, being formedwith flattened portions providing plane surfaces upon four sides thereof, said flattened portions being of slightly greater depth than the depth of thethreads whereby the distance between the diameter of the screw, a plurality of spaced lands being formed between adjacent ones of said plane surfaces, said lands being provided with screw threads which diminish in depth toward the blunt entering end of the screw, whereby the lands and the flattened surfaces merge at said end of the screw to provide an end'surface which is approximately in the form of a square with rounded corners, said corners providing self-centering means for facilitating the application of the screw to said opening, and the advancing margins of the gradually threaded lands serving as cutting edges to form threads in the'wall of said opening. I

2. A self-tapping screw fastener of the kind described having a head, a cylindrical shank constituting a holding portion formed with continuthe blunt ,en'tering end to the thread-holding.

portion, and cutting threads on said corners whereby a self-centering blunt-ended screw with a thread-cutting portion and acontinuous 3. Aself-tapping screw fastener of the kind-described having a head, a cylindrical shank divided into a continuous thread-holding portion and a relatively short thread-cutting portion, said thread-cutting portion constituting means for automatically self-centering the screw when applied to a. pre-formed opening, the self-centering and cutting portions consisting of four fiat flared faces at the entering end, and four flared threadcutting portions on the corners between said flat faces.

FRANK k. BROWN. 

